Die cutting machines are used to cut corrugated and solid fibre sheet stock into irregular shaped carton blanks. The sheet stock is characterized by having several plies of paper stock laminated together to form either corrugated or solid fibre sheets. The irregular shaped carton blanks are folded after die cutting to form cartons for the shipment of goods, point of sale displays, advertising displays, carton separators, and the like.
Die cut sheets are customarily scored to facilitate folding into the desired carton or other shapes. Depending on the characteristics of the stock, the sheets are sometimes difficult to fold along the scores; that is, the folds do not always follow the score lines exactly. Thus, it is often desirable to slit through several plies of the sheets, leaving one or more plies uncut. The sheets then fold very precisely along the slit.
Die cutting is accomplished either by a flat bed die cutter or by a rotary die cutter. An example of a flat bed die cutter is shown in U.S. Pat. No. 3,606,824. An example of a rotary die cutter is shown in U.S. Pat. No. 4,240,312.
Flat bed die cutters almost always cut steel-to-steel; that is, the cutting dies are straight edged rules which cut through the stock and against a steel platen. Most rotary die cutters use serrated edged rules which cut through the stock and into a soft rotating anvil although some use straight edged rules which cut against a hardened steel rotary anvil.
This invention is primarily concerned with soft anvil rotary die cutting although it may be applied to flat bed die cutters and rotary steel-to-steel (hard anvil) die cutters with equally satisfactory results.
Until now, slitting selected plies, that is, cutting part way through the stock, has been virtually impossible because the soft anvil deforms or gives beneath the slitting blade. Therefore, in effect, the thickness of the stock varies along the length of cut and uniform depths of cuts cannot be made. This occurs because the soft surface of the anvil may be irregular due to wear from previous die cutting coupled with its tendency to give beneath the cutting rule. Uniform depth's of cuts are also difficult to achieve on flat bed die cutters because the top plies of the stock sometimes tend to deform irregularly beneath the slitting rule whereas, when the stock is die cut completely through, the stock is pinched between the rule and anvil. The same is true on steel-to-steel rotary die cutters.
Accordingly, an object of this invention is to provide a method and apparatus for slitting selected plies of multiply sheets. More particulary, another object is to provide apparatus for simultaneously compressing and slitting such sheets, such compression being effective to achieve uniform depths of cuts by the slitting rules or knives. A still further object is to provide such slitting and scoring apparatus for flat bed die cutters and steel-to-steel rotary die cutters as well as soft anvil rotary die cutters.
These and other objects and novel features are generally accomplished by the invention, a summary of which appears below.